1. Field of the Invention
The present invention relates to a frequency characteristics determination device, and more specifically, relates to the frequency characteristics determination device for determining a frequency response curve of an audio signal.
2. Description of the Related Art
Equalizers change sound quality of audio signals according to predetermined frequency response curves. The equalizers contain a frequency characteristics determination device for determining frequency characteristics of audio signals, and use a frequency response curve determined by a frequency characteristics determination device.
Various methods for determining frequency characteristics are present. For example, a method for dividing an audio signal into a plurality of frequency bands, and determining a gain for each of the divided frequency bands is present.
Further, Japanese Unexamined Patent Application Publication No. 2011-517390 discloses a method for generating a curve that connects points specified by a user, and using the generated curve as a frequency response curve. In the invention of Japanese Unexamined Patent Application Publication No. 2011-517390, a plane where a frequency is set along an abscissa axis and a gain is set along an ordinate axis is displayed on a display. The user specifies desired points on the displayed plane. A curve that smoothly connects the specified points is automatically generated. An equalizer uses the generated curve as a frequency response curve.
In Japanese Unexamined Patent Application Publication No. 2011-517390, the frequency response curve is generated based on a frequency response of a shelving filter. Japanese Patent No. 4132693 discloses an equalizer for connecting specified points using spline interpolation so as to generate a frequency response curve.
A frequency characteristics determination device can generate a curve for smoothly connecting a plurality of specified points using a Bezier curve, and determine this curve as a frequency response curve. However, when the frequency response curve is generated by using the Bezier curve, the generated frequency response curve occasionally has an unnatural shape. For example, a generated frequency response curve occasionally draws a loop or an extremely large peak.
When the frequency response curve draws a loop, gains cannot be uniquely specified for a certain frequency. Further, when a frequency response curve draws an extremely large peak, an audio with a frequency related to the peak is enhanced beyond expectation, and an audio signal cannot be changed into one with a sound quality intended by a user.